1. Field of the Invention
This invention relates to the monitoring of peer to peer links in a wireless network, and in particular to the determination of an optimal network structure in dependence upon the monitored quality of these links. The invention is particularly well suited for wireless systems having a centralized control station, and is further well suited for wireless ATM (Asynchronous Transfer Mode) networks.
2. Discussion of the Related Art
A communications network requires a network protocol to operate effectively and efficiently. One such protocol for a wireless network is a contention based protocol. In a contention based protocol network, any station is free to transmit whenever another station is not currently transmitting. Such a protocol, however, exhibits inefficiencies due to collisions, wherein two transmitters attempt to initiate transmission at the same time. The likelihood of collisions increase with an increase in network traffic, making contention based protocols inefficient for high traffic networks. Because collisions may occur, and will be undetectable by each of the transmitters, the contention based protocol typically requires an acknowledgment from the intended receiver to the transmitter, further limiting the network""s efficiency, and further increasing the likelihood of collisions.
An alternative to a contention based protocol is a centralized control protocol, wherein one station in the network determines when each of the other stations may transmit. Each station transmits only during its allocated time, thereby eliminating the possibility of collisions, and thereby increasing the efficiency of the network. The communication of the information related to the control of the network incurs an overhead inefficiency, but this overhead is relatively independent of the quantity of communications on the network. Therefore, the centralized control protocol is particularly well suited for high traffic networks, or networks which require a deterministic quality of service (QoS), such as ATM.
An essential element to a centralized control protocol is that each station on the network must be able to communicate with the centralized controller. Wireless networks, however, often support mobile stations, and the ability to communicate between the controller and the mobile station must be assured regardless of the location of mobile station. One architecture commonly utilized is a cellular network, wherein central controllers are placed throughout a region, each central controller having a local transmission area, or cell, within which communications with a station can be expected to be reliable. The central controllers are placed such that any point in the region lies within at least one cell. Such a cellular approach, however, requires that the central controllers be stationary, and does not readily allow for a wireless communications network within which all stations may be mobile.
To support a wireless network having a centralized control structure, yet still allow for freedom of movement amongst all the stations on the network, the control structure should be reconfigurable, in dependence upon the changing environment. If communications within the current structure are poor, the structure should be changed to one which provides for a higher quality of communications. To effect such a reconfigurable network, a means must be provided to assess the quality of the existing network structure, and also to estimate the quality of an alternative network structure.
An object of this invention is to provide a method and apparatus for determining the quality of the communication paths within a network. It is a further object of this invention to utilize this quality determination to optimize the structure of the network. It is a further object of this invention to utilize this quality determination to establish optimized paths for retransmission links within the network.
The quality of the communication paths within a network is determined by having each station within the network monitor and assess the quality of reception of transmissions from each of the other stations within the network. These individual quality assessments are forwarded, periodically or on demand, to a centralized controller. These assessments then form a matrix of quality assessments, from which the structure of the network can be optimized, by selecting, for example, the station having the overall best quality measure relative to each of the others. The network is thereafter reconfigured to replace the current, sub-optimal, centralized control station with the selected station.
The matrix of quality assessments can also be utilized to identify problematic terminal-to-terminal links, and to institute retransmission relay paths to overcome the poor quality links.